1. Field of the Invention
This invention relates to the field of electro mechanics. More particularly, this invention relates to the field of safe and arm devices. Still more particularly, but without limitation thereto, this invention relates to the field of electro-mechanical safe and arm devices for detonating a booster in a bomb.
2. Description of the Prior Art
One of the most critical elements in conventional ordnance is the safe and arm device (S-A). The primary function of the S-A is to maintain the weapon in a safe condition until an arming signal is received. Upon receipt of the arming signal, the S-A transforms the weapon from a safe condition into an armed condition where the main explosive charge may be detonated.
These functions are normally performed by controlling the alignment of the sensitive explosive components of the warhead initiation system. In the safe position the primary initiation explosives are misaligned with the booster/warhead explosives, preventing detonation prior to arming. Arming is started when the fuze receives a unique set of inputs indicating release from the aircraft. Upon obtaining a safe separation distance or time, the initiation explosives are aligned with the booster/warhead explosives. In this position, initiation of the sensitive explosives will cause the warhead to detonate. Initiation in the safe condition will result in a dud weapon with no booster/warhead detonation.
Current bomb S-A devices are marginal in meeting both the safety and arming requirements. The safety failures experienced have resulted in many bomb fuzes being removed from active service as a result of loss of both aircraft and personnel. Arming failures and inability to survive impact in the armed condition have resulted in a low weapon reliability and high dud rate. The net result is a low weapon effectiveness and a high risk of usage for bombs.
Current bomb fuze safe and arm (S-A) devices utilize either mechanical escapements or electronic timers to provide safe separation arming time delays. Also, many of the S-A designs employ stored energy, such as bellows motors, to arm the fuze. These techniques have proven to present safety harzards and yield low reliability in previous bomb fuzes.
The use of mechanical escapements as a safe-arm time delay is undesirable for two major reasons. First, the escapement mechanism technology is rapidly disappearing with the advent of the digital watch technology, resulting in a sharp decrease in manufacturing capabilities coupled with a rise in costs. Second, the flexibility of mechanical timers is poor, resulting in a high cost for arming time options with relatively poor timing accuracy. The advantage in using a mechanical interlock is that it provides a high degree of safety unless the escapement goes into a "runaway" condition and functions improperly.
In contrast to the mechanical escapement, the electronic timer can provide a very accurate reference time. Unfortunately electronic timers do not provide a mechanical interlock and have failure modes which allow instantaneous arming.
Another problem is experienced when existing designs are used with moderate or hard target penetrators. Upon impact the high accelerations tend to either destroy the S-A mechanism or cause misalignment of the explosive output. This results in low reliability with the bomb/fuze combination being unsatisfactory.